Gas-filled discharge tube



May 18, 1937.

J. G. w. MULDER 2,080,628 GAS-FILLED DISCHARGE TUBE 2 Sheets-Sheet 1 Filed Dec. 23, 1931 J6. ZaMaZd'er,

May 18, 1937.. J. G. w. MULDER GAS-FILLED DISCHARGE TUBE Filed Dec. 23, 1951 2 Sheets-$heet 2 Patented May 18, 1937 UNITED STATES PATENT OFFIQE GAS-FILLED DISCHARGE TUBE Application December 23, 1931, Serial No. 582,825 In Germany January 26, 1931 7 Claims.

This invention relates to a discharge tube comprising one or more anodes and an incandescible cathode, preferably an oxide cathode, as the source of electrons. The filling of the discharge tube consists partly or wholly of a vapour, for example mercury vapour, or of a mixture of vapours with or without the addition of one or more gases.

Discharge tubes of this kind are very frequently used for rectifying alternating current, although they are also used for other purposes.

The invention has for its object to increase the life of the incandescible cathode of discharge tubes designed for more than 10,000 volts and more than 10 amperes. In discharge tubes operating on such high voltages the life of the incandescible cathode is materially shorter than in the case of low-voltage tubes of the same type. This is due to the fact that in high-voltage tubes a very low vapor pressure is required to prevent undesired discharges, and this low pressure is largely responsible for the disintegration of the cathode.

The discharge tube according to the invention is characterized by the feature that the discharge between the anode and the cathode passes through one or more chambers for the condensation of the vapour. This permits maintaining in the cathode chamber a comparatively high pressure, which avoids excessive disintegration of the cathode, whereas the pressure in the anode chamber is kept very low as the vapour condenses before reaching this chamber. Although in the forms of construction hereinafter described only a single anode is shown, it is obvious that the same principles may be applied in the case of a plurality of anodes. In this case the discharge path to each anode may comprise an individual chamber or a plurality of individual condensing chambers, or again one or more condensing chambers common to all the discharge paths may be used.

In discharge tubes designed for the reception or amplification of signals which use a so-called gaseous cathode and in which small currents are controlled by a control grid, and which tubes are used to amplify signals, it has already been suggested to condense the vapor between the anode and the cathode. However, in thiscase the electrons for the main discharge are obtained from an auxiliary discharge, which is initiated in a vapor-filled chamber. In such case the condensation is to prevent ionization in the chamber in which the control grid is disposed, as otherwise the control by means of the grid would be rendered impossible.

As stated above, according to the invention there is a condensation chamber for the metal vapour. The discharge tube consists consequently of alternate restricted and enlarged parts. It is well known that the ignition is rendered very difiicult by the contractions of the tube wall. It is possible to overcome this difficulty by a suitable form of construction in which the wall of the discharge tube comprises one or more metal portions and in which a chamber, situated preferably between two successive metal wall portions of the discharge tube, is of sufficiently large cross-section to cause the vapour to condense in it. Although with the discharge tubes according to the invention artificial coolers for the condensing chamber may be important, they are superfluous in the form of construction described. Furthermore it is preferable for the discharge tube to be so shaped that the discharge path between the cathode and the anode forms one or more preferably acute angles. For this purpose the discharge tube may consist of a cathode chamber and of one or more condensation chambers arranged alongside the cathode chamber; in addition an anode chamber is provided above the last condensing chamber and the chambers are connected successively by insert tubes for the passage of the discharge. The bend in the discharge path makes it very difficult for the high-speed positive ion emanating from the anode chamber to reach the cathode so that the risk of disintegration of the incandescible cathode by impact of ions is decreased. Besides, these ions are slowed down in their travel by the increase in gas pressure which exists in the direction to the cathode. In addition, the bending of the discharge path is important because the difference in gas pressure between the various chambers is increased, because of the change in the direction of the flow of vapor,

The condensation chambers and the cathode chamber are preferably not only connected by the tubes for the discharge but also successively connected at their lower ends by return conduits for the condensate. These conduits are preferably provided with one or more bends to dampen the flow of the condensate therethrough. If the conduits were not provided with such bends, an increase in the vapor pressure Within the cathode chamber would occur each time a drop of condensate falls to the bottom of the condensation chamber. I

In another form of construction, the cathode chamber, condensation chambers, and the anode chamber are arranged one above the other. In this case one or more hoods are provided to prevent the condensate flowing back to the cathode chamber, from coming into contact with the cathode.

Those portions of the discharge tube in which the condensate collects are preferably provided with contractions or re-entrant parts to secure a high level of the collecting condensate even with a small amount thereof.

.In order that the invention may be clearly understood and readily carried into effect three forms of construction in accordance therewith will now be described more fully with reference to the accompanying drawings, in which Figure 1 is a sectionized side view of a discharge tube in which the cathode chamber is arranged at the side of the condensation chamber,

Figure 2 is a sectionized side view of a discharge tube in which the various chambers are arranged one above the other, and

Figure 3 is a sectionized side view of a discharge tube in accordance with another embodiment of the invention.

Referring to Figure 1, a press 2 in the cathode chamber I supports an incandescible cathode 3.

The cathode consists of a piece of rolled wire gauze 4 the successive convolutions of which are spaced apart at some intermediate distance, the coils of a heating helix being laid around the aggregate which is coated both internally and externally with a substance of high emissive power for instance with a suitable oxide coating. A cathode of this kind has a very high electron emission.

At the bottom of the cathode chamber .I is a supply of mercury 5. The cathode chamber communicates through a tube 6 with the condensa tion chamber I. The tube 6 consists of ferrochrome and is sealed on each side to the glass of the discharge tube. In addition, the chambers I and 1 are connected by means of a tube 8 to form a communicating vessel for the mercury.

The condensation chamber 1 communicates by means of a ferrochrome tube 9 with the anode chamber ID. The anode II is suitably supported, for example, by a ferrochrome plate I2 having its circumference sealed to the glass of the tube and the leading-in conductor connected to the plate.

Due to the presence of the incandescible cathode 3 in the cathode chamber I, the temperature and thus the vapor pressure of the mercury in this chamber is comparatively high. The mercury vapor which passes from the cathode chamber to the anode chamber I0 condenses, however, in the chamber I. This'chamber always remains comparatively cool as it is remote from the incandescible cathode and has a large surface which readily dissipates the heat to the surrounding air. The tube 8 enables the condensed mercury to fiow back to the cathode chamber. A U-shaped portion I 4 of the tube 8 dampens the flow of mercury so that fluctuating movements of the liquid and the variations in pressure incidental thereto are avoided. Consequently, a very low pressure prevails in the anode chamber so that the risk of flashing over is reduced to a minimum. Each of the chambers I and I comprises a re-entrant part I3 that constitutes a core. The mercury has consequently a high level while the amount of mercury is kept small. At the same time in spite of the small quantity of mercury in chamber I a large area of mercury can be heated by the cathode 3.

The tubes 6 and 9 are provided with leads 2!] and 2| respectively and may be connected to a suitable voltage which permits the starting potential to be considerably reduced. The voltage applied to these tubes generally falls between that of the anode and that of the cathode, and may be obtained, for example, from a separate secondary coil on the filament supply transformer.

In addition, by applying a direct voltage between the anode and the cathode and an alternating voltage to the tubes 6 and 9 it is possible to transform a direct current into an alternating current.

In Figure 2 like parts are designated by the same reference numerals as those used in Figure l. The construction shown in Fig. 2 mainly differs from that in Figure 1 in that the discharge path has no bend, but the various chambers are arranged in axial alignment with each other. However should the mercury which condenses in the condensation chamber I and drips down, find it way to the incandescible cathode, this would cause a rapid deterioration at those points of the cathode on which mercury settles. To prevent this the ferrochrome tube 6 is provided with two internal and upward tapering tubes I5 and I6 made of the same metal. Thus, the mercury condensing in the chamber I is guided to flow between the tube I5 and the wall of the discharge tube and thence down along the wall of the tube 6 and along the exterior of the tube I6. The tube I6 forms a hood over the incandescible cathode so that dripping down of the mercury on the cathode is prevented.

In some instances, the tubes I5 and I6, having a high temperature, may cause the mercury drops coming into contact with them to volatilize. This has the drawback that it leads to sudden increases in pressure. In order to lessen this disadvantage, the tubes I5 and I6 may be instead of metal, for example of quartz. Or as shown in Figure 3, the condensed mercury may be returned to the chamber I through a circulating conduit I1. In such a construction a hood I8 may be useful in protecting the seal II! from excessive heating. In addition, such a hood is adapted to improve the ignition. Similar services are also rendered by the hood I6 in Figure 2.

In some instances it is sufficient to have only one of the restricted wall portions of metal.

In addition to a vapour, one or more gases, preferably rare gases, may be enclosed within the tube.

Discharge tubes according to the invention can be'constructed, for example, for voltages of kilovolts and for discharge currents of 1 amp., and their life may be over 2000 hours. These values may be materially increased.

What I claim is:-

1. A discharge tube comprising a vapor filling, a large diameter glass bulb for serving as a condensation vessel, a second glass bulb containing a highly electron-emissive cathode and a quantity of the material of the filling in its nonvaporized state, a third glass bulb containing an anode and having a substantially smaller diameter than said first bulb, and two metal tubes having a diameter less than the diameter of said first bulb, each of said tubes connecting in a hermetical manner said first bulb to one of said latter two bulbs, the axes of said tubes forming an acute angle.

2.. A discharge tube comprising a vapor filling,

a large diameter glass bulb serving as a condensation vessel, a second glass bulb containing a high- 1y electron-emissive cathode and a quantity of the material of the filling in its liquid form, a third glass bulb containing an anode and having a substantially smaller diameter than said first bulb, two metal tubes having a diameter less than the diameter of said first bulb, each of said tubes connecting in a hermetical manner said first bulb to one of said two latter bulbs, the axis of said tubes forming an acute angle, and a return tube having a loop, said return tube being connected between the bottom portions of said first and second bulbs to allow the condensate to return to said second bulb.

3. A discharge tube comprising an anode, and incandescible oxide cathode, a gaseous filling consisting partly of mercury vapor, an enclosure for the cathode, an enclosure for the anode, a condensation enclosure between said cathode and anode enclosures, a tube connecting said anode enclosure to said condensation enclosure, and a second tube connecting said cathode enclosure to said condensation enclosure, said tubes having a smaller cross section than that of the condensation enclosure, the axes of said tubes forming an acute angle with each other.

4. A discharge tube comprising an anode, an incandescible oxide cathode, a filling consisting partly of vapor, an enclosure for said cathode, an enclosure for said anode, a condensation enclosure in axial alignment with said anode enclosure, and tubes individually connecting the condensation enclosure with the cathode and anode enclosures and having a smaller cross-section than the condensation enclosure, the axis of the tube connecting the condensation enclosure to the cathode enclosure forming an acute angle with the common axis of the anode enclosure and the condensation enclosure.

5. A rectifier tube having a cathode of high electron-emitting capacity, an anode, an enclosure for the anode, a condensation enclosure, an enclosure for the cathode, said anode and condensation enclosures being in axial alignment, said cathode enclosure being disposed laterally from said anode and condensation enclosures and spaced therefrom, a metal tube connecting the cathode enclosure to the condensation enclosure, and a second metal tube connecting the anode enclosure to the condensation enclosure, said tubes having a smaller cross section than that of the condensation enclosure.

6. A rectifier tube for high voltages comprising a high electron-emitting cathode, an anode, a filling consisting partly of vapor, an enclosure for the cathode, an enclosure for the anode, a condensation enclosure for the vapor and interposed between the cathode and anode enclosures, metal tubes connecting said condensation enclosure to said cathode and anode enclosures and having a smaller cross-section than the condensation enclosure, the main discharge path between said cathode and anode leading from said cathode enclosures through said condensation enclosure to said anode enclosure, and a tube having a U-shaped bend and connecting the bottom of said condensation enclosure to the bottom of said cathode enclosure for the return of condensate to said cathode enclosure.

7. A discharge tube having a cathode, an anode, a filling comprising a vapor, an enclosure for the cathode, an enclosure for the anode, an enclosure intermediate between the anode and cathode enclosures for the condensation of said vapor, metal tubes connecting said condensation enclosure with the other enclosures and having a smaller cross-section than the condensation enclosure, the main discharge path between said cathode and anode leading from saidcathode enclosure through said condensation enclosure to said anode enclosure, and a tube for the return of the condensate to said cathode enclosure, said return tube being provided with a loop and connecting the bottom part of said condensation enclosure to the bottom part of said cathode enclosure.

JOl-IANNES GIJSBERTUS WILI-IELM MULDER. 

